1. Field of the Invention
This invention relates, for example, to a memory cartridge and a system using the same.
2. Related Background Art
Recent years have seen the development of a scanning tunneling microscope (hereinafter referred to as the STM) through which electron structure on and near the surface of a substance can be directly observed (G. Binnig et al., Helvetica Physica Acta, 55, 726 (1982), and irrespective of single crystal or amorphous materials, it has become possible to observe a real spatial image with high resolving power and moreover, this microscope has the advantage that measurement can be accomplished with low electric power almost without imparting damage by electric current to the sample substance and further, this microscope operates not only in super-high vacuum but also in the atmosphere and solution and can be applied to various materials and therefore, wide application thereof is expected.
The STM utilizes the phenomenon that when a voltage is applied between a conductive probe and an electrically conductive sample and the probe is brought close to a distance of about 1 nm, the tunnel current starts flowing. Recently, as disclosed, for example, in Japanese Laid-Open Patent Application No. 63-161552 and Japanese Laid-Open Patent Application No. 63-161553, there have been made numerous propositions to apply the principle of this STM to construct a memory apparatus chiefly for super-high density recording and reproduction. That is, if use is made of a method in which by a probe electrode corresponding to the probe of the STM, physical deformation is imparted to a recording medium corresponding to a sample, or the electron state of the surface of the medium is changed to record information and the information of recording bits is reproduced by a tunnel current flowing between the two, it is considered that large-scale information can be recorded and reproduced at a high density of the order of molecule or atom.
It has recently been reported that in the above-described recording method, to impart physical deformation, besides an acute recording probe being pressed against the recording medium, a pulse voltage can be applied onto a recording material of graphite or the like to thereby form a hole therein. That is, the probe electrode is brought close to the surface of the recording medium, and then the application of a voltage is effected between the two with 3-8 V and a pulse width of 1-100 .mu.s, whereby a hole of a diameter of about 40 .ANG. can be formed, and such hole can be sufficiently used as a recording bit. On the other hand, to change the electron state to accomplish recording, there is known a method whereby cumulative film of appropriate organic molecules is made on a ground electrode by the Langmuir-Blodgett's technique (hereinafter referred to as the LB technique) or the like and a voltage is applied between the ground electrode and the probe electrode to vary the electrical resistance characteristic of this minute portion, and attention is paid to this method because of the ease of erasing and rewriting.
FIG. 6 of the accompanying drawings shows the construction of a memory apparatus according to the prior art in which the electron state is changed to effect recording. On a movable substrate 2 provided on a coarse movement mechanism 1, there are placed a ground electrode 3 and a recording medium 4 having a switching memory effect, and a probe electrode 6 attached to a three-dimensional (3-D) driving mechanism 5 is provided in opposed relationship with the recording medium 4, and the coarse movement mechanism 1 is first driven by a microcomputer 7 and a coarse movement control circuit 8, whereby rough alignment of the probe electrode 6 and the recording medium 4 is accomplished. During recording, when the three-dimensional driving mechanism 5 is driven by an XY scan driving circuit 9 to scan the probe electrode 6 on the recording medium 4 and at a recording position, a pulse voltage is applied to the probe electrode 6 and the ground electrode 3 by a voltage applying circuit 10, regions locally differing in electrical resistance from one another are created in the recording medium 4 and recording is effected.
During reproduction, the probe electrode 6 is scanned on the surface of the recording medium 4 while such a degree of constant voltage that a tunnel current flows is applied between the probe electrode 6 and the recording medium 4. The tunnel current obtained at that time is amplified and detected by a current amplifier 11, and the three-dimensional driving mechanism 5 is driven by a servo circuit 12 so that the tunnel current may always assume a predetermined value, whereby the probe electrode 6 is moved in a vertical direction, and the amount of movement in this vertical direction corresponds to recording information. All these controls are effected by the microcomputer 7.
As described above, to utilize the tunnel current, it is necessary that the probe electrode is brought close to the recording medium 4 up to about 1 nm, and a highly accurate working and manufacturing technique is required of the probe electrode 6 and the recording medium 4.
However, to put the recording and reproducing method as described above into practical use, it is of course necessary to accomplish very highly accurate and quick position adjustment (tracking) of the probe electrode 6 and the recording medium 4 during the interchange of the recording medium 4, and if the temperature of the apparatus changes, the movable substrate 2 on which the recording medium 4 is placed 10 and the region to which the probe electrode 6 is attached will thermally expand and the relative position of the recording medium 4 and the probe electrode 6 will shift, and this leads to the risk of causing an error to recording and reproduction.
This is a great problem particularly in a so-called multiprobe system wherein multiple probes are parallel-disposed. The multiprobe system is large in its area in XY direction because multiple probes are parallel-disposed therein, and when generally viewed, there is great amount of variation by a temperature change in this system. Assuming that a temperature change has occurred and the intervals between the adjacent probes have changed, even if a certain probe is tracked to a prescribed position on the recording medium, the other probes will deviate from the prescribed position.